Genus

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The hierarchy of biological classification's eight major taxonomic ranks. A family contains one or more genera. Intermediate minor rankings are not shown. Biological classification L Pengo vflip.svg DomainKingdomClassOrderFamily
The hierarchy of biological classification's eight major taxonomic ranks. A family contains one or more genera. Intermediate minor rankings are not shown.

Genus ( /ˈdʒiːnəs/ plural genera /ˈdʒɛnərə/ ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. [1] In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.

Contents

E.g. Panthera leo (lion) and Panthera onca (jaguar) are two species within the genus Panthera . Panthera is a genus within the family Felidae.

The composition of a genus is determined by taxonomists. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, [2] [3] including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful:

  1. monophyly – all descendants of an ancestral taxon are grouped together (i.e. phylogenetic analysis should clearly demonstrate both monophyly and validity as a separate lineage).
  2. reasonable compactness – a genus should not be expanded needlessly.
  3. distinctness – with respect to evolutionarily relevant criteria, i.e. ecology, morphology, or biogeography; DNA sequences are a consequence rather than a condition of diverging evolutionary lineages except in cases where they directly inhibit gene flow (e.g. postzygotic barriers).

Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera. [4]

Etymology

The term "genus" comes from the Greek γένος , a noun form cognate with gignere ('to bear; to give birth to'). The Swedish taxonomist Carl Linnaeus popularized its use in his 1753 Species Plantarum , but the French botanist Joseph Pitton de Tournefort (1656–1708) is considered "the founder of the modern concept of genera". [5]

Use

The scientific name (or the scientific epithet) of a genus is also called the generic name; in modern style guides and science, it is always capitalised. It plays a fundamental role in binomial nomenclature, the system of naming organisms, where it is combined with the scientific name of a species: see Botanical name and Specific name (zoology).[ citation needed ]

Use in nomenclature

The rules for the scientific names of organisms are laid down in the nomenclature codes, which allow each species a single unique name that, for animals (including protists), plants (also including algae and fungi) and prokaryotes (bacteria and archaea), is Latin and binomial in form; this contrasts with common or vernacular names, which are non-standardized, can be non-unique, and typically also vary by country and language of usage.

Except for viruses, the standard format for a species name comprises the generic name, indicating the genus to which the species belongs, followed by the specific epithet, which (within that genus) is unique to the species. For example, the gray wolf's scientific name is Canis lupus, with Canis (Latin for 'dog') being the generic name shared by the wolf's close relatives and lupus (Latin for 'wolf') being the specific name particular to the wolf. A botanical example would be Hibiscus arnottianus , a particular species of the genus Hibiscus native to Hawaii. The specific name is written in lower-case and may be followed by subspecies names in zoology or a variety of infraspecific names in botany.

When the generic name is already known from context, it may be shortened to its initial letter, for example, C. lupus in place of Canis lupus. Where species are further subdivided, the generic name (or its abbreviated form) still forms the leading portion of the scientific name, for example, Canis lupus lupus for the Eurasian wolf subspecies, or as a botanical example, Hibiscus arnottianus ssp. immaculatus. Also, as visible in the above examples, the Latinised portions of the scientific names of genera and their included species (and infraspecies, where applicable) are, by convention, written in italics.

The scientific names of virus species are descriptive, not binomial in form, and may or may not incorporate an indication of their containing genus; for example, the virus species "Salmonid herpesvirus 1", "Salmonid herpesvirus 2" and "Salmonid herpesvirus 3" are all within the genus Salmonivirus ; however, the genus to which the species with the formal names "Everglades virus" and "Ross River virus" are assigned is Alphavirus .

As with scientific names at other ranks, in all groups other than viruses, names of genera may be cited with their authorities, typically in the form "author, year" in zoology, and "standard abbreviated author name" in botany. Thus in the examples above, the genus Canis would be cited in full as "Canis Linnaeus, 1758" (zoological usage), while Hibiscus, also first established by Linnaeus but in 1753, is simply "Hibiscus L." (botanical usage).

The type concept

Each genus should have a designated type, although in practice there is a backlog of older names without one. In zoology, this is the type species, and the generic name is permanently associated with the type specimen of its type species. Should the specimen turn out to be assignable to another genus, the generic name linked to it becomes a junior synonym and the remaining taxa in the former genus need to be reassessed.

Categories of generic name

In zoological usage, taxonomic names, including those of genera, are classified as "available" or "unavailable". Available names are those published in accordance with the International Code of Zoological Nomenclature; the earliest such name for any taxon (for example, a genus) should then be selected as the "valid" (i.e., current or accepted) name for the taxon in question.

Consequently, there will be more available names than valid names at any point in time, which names are currently in use depending on the judgement of taxonomists in either combining taxa described under multiple names, or splitting taxa which may bring available names previously treated as synonyms back into use. "Unavailable" names in zoology comprise names that either were not published according to the provisions of the ICZN Code, e.g., incorrect original or subsequent spellings, names published only in a thesis, and generic names published after 1930 with no type species indicated. [6] According to "Glossary" section of the zoological Code, suppressed names (per published "Opinions" of the International Commission of Zoological Nomenclature) remain available but cannot be used as the valid name for a taxon; however, the names published in suppressed works are made unavailable via the relevant Opinion dealing with the work in question.

In botany, similar concepts exist but with different labels. The botanical equivalent of zoology's "available name" is a validly published name. An invalidly published name is a nomen invalidum or nom. inval.; a rejected name is a nomen rejiciendum or nom. rej.; a later homonym of a validly published name is a nomen illegitimum or nom. illeg.; for a full list refer to the International Code of Nomenclature for algae, fungi, and plants and the work cited above by Hawksworth, 2010. [6] In place of the "valid taxon" in zoology, the nearest equivalent in botany is "correct name" or "current name" which can, again, differ or change with alternative taxonomic treatments or new information that results in previously accepted genera being combined or split.

Prokaryote and virus codes of nomenclature also exist which serve as a reference for designating currently accepted genus names as opposed to others which may be either reduced to synonymy, or, in the case of prokaryotes, relegated to a status of "names without standing in prokaryotic nomenclature".

An available (zoological) or validly published (botanical) name that has been historically applied to a genus but is not regarded as the accepted (current/valid) name for the taxon is termed a synonym; some authors also include unavailable names in lists of synonyms as well as available names, such as misspellings, names previously published without fulfilling all of the requirements of the relevant nomenclatural code, and rejected or suppressed names.

A particular genus name may have zero to many synonyms, the latter case generally if the genus has been known for a long time and redescribed as new by a range of subsequent workers, or if a range of genera previously considered separate taxa have subsequently been consolidated into one. For example, the World Register of Marine Species presently lists 8 genus-level synonyms for the sperm whale genus Physeter Linnaeus, 1758, [7] and 13 for the bivalve genus Pecten O.F. Müller, 1776. [8]

Identical names (homonyms)

Within the same kingdom, one generic name can apply to one genus only. However, many names have been assigned (usually unintentionally) to two or more different genera. For example, the platypus belongs to the genus Ornithorhynchus although George Shaw named it Platypus in 1799 (these two names are thus synonyms). However, the name Platypus had already been given to a group of ambrosia beetles by Johann Friedrich Wilhelm Herbst in 1793. A name that means two different things is a homonym. Since beetles and platypuses are both members of the kingdom Animalia, the name could not be used for both. Johann Friedrich Blumenbach published the replacement name Ornithorhynchus in 1800.

However, a genus in one kingdom is allowed to bear a scientific name that is in use as a generic name (or the name of a taxon in another rank) in a kingdom that is governed by a different nomenclature code. Names with the same form but applying to different taxa are called "homonyms". Although this is discouraged by both the International Code of Zoological Nomenclature and the International Code of Nomenclature for algae, fungi, and plants, there are some five thousand such names in use in more than one kingdom. For instance,

A list of generic homonyms (with their authorities), including both available (validly published) and selected unavailable names, has been compiled by the Interim Register of Marine and Nonmarine Genera (IRMNG). [9]

Use in higher classifications

The type genus forms the base for higher taxonomic ranks, such as the family name Canidae ("Canids") based on Canis. However, this does not typically ascend more than one or two levels: the order to which dogs and wolves belong is Carnivora ("Carnivores").

Numbers of accepted genera

The numbers of either accepted, or all published genus names is not known precisely; Rees et al., 2020 estimate that approximately 310,000 accepted names (valid taxa) may exist, out of a total of c. 520,000 published names (including synonyms) as at end 2019, increasing at some 2,500 published generic names per year. [10] "Official" registers of taxon names at all ranks, including genera, exist for a few groups only such as viruses [1] and prokaryotes, [11] while for others there are compendia with no "official" standing such as Index Fungorum for fungi, [12] Index Nominum Algarum [13] and AlgaeBase [14] for algae, Index Nominum Genericorum [15] and the International Plant Names Index [16] for plants in general, and ferns through angiosperms, respectively, and Nomenclator Zoologicus [17] and the Index to Organism Names for zoological names.

Totals for both "all names" and estimates for "accepted names" as held in the Interim Register of Marine and Nonmarine Genera (IRMNG) are broken down further in the publication by Rees et al., 2020 cited above. The accepted names estimates are as follows, broken down by kingdom:

Estimated accepted genus totals by kingdom - based on Rees et al., 2020 Estimated accepted genus totals by kingdom - based on Rees et al 2020.jpg
Estimated accepted genus totals by kingdom - based on Rees et al., 2020

The cited ranges of uncertainty arise because IRMNG lists "uncertain" names (not researched therein) in addition to known "accepted" names; the values quoted are the mean of "accepted" names alone (all "uncertain" names treated as unaccepted) and "accepted + uncertain" names (all "uncertain" names treated as accepted), with the associated range of uncertainty indicating these two extremes.

Within Animalia, the largest phylum is Arthropoda, with 151,697 ± 33,160 accepted genus names, of which 114,387 ± 27,654 are insects (class Insecta). Within Plantae, Tracheophyta (vascular plants) make up the largest component, with 23,236 ± 5,379 accepted genus names, of which 20,845 ± 4,494 are angiosperms (superclass Angiospermae).

By comparison, the 2018 annual edition of the Catalogue of Life (estimated >90% complete, for extant species in the main) contains currently 175,363 "accepted" genus names for 1,744,204 living and 59,284 extinct species, [18] also including genus names only (no species) for some groups.

Genus size

Number of reptile genera with a given number of species. Most genera have only one or a few species but a few may have hundreds. Based on data from the Reptile Database (as of May 2015). Number of reptile genera with a given number of species.png
Number of reptile genera with a given number of species. Most genera have only one or a few species but a few may have hundreds. Based on data from the Reptile Database (as of May 2015).

The number of species in genera varies considerably among taxonomic groups. For instance, among (non-avian) reptiles, which have about 1180 genera, the most (>300) have only 1 species, ~360 have between 2 and 4 species, 260 have 5–10 species, ~200 have 11–50 species, and only 27 genera have more than 50 species. However, some insect genera such as the bee genera Lasioglossum and Andrena have over 1000 species each. The largest flowering plant genus, Astragalus , contains over 3,000 species. [19]

Which species are assigned to a genus is somewhat arbitrary. Although all species within a genus are supposed to be "similar", there are no objective criteria for grouping species into genera. There is much debate among zoologists whether enormous, species-rich genera should be maintained, as it is extremely difficult to come up with identification keys or even character sets that distinguish all species. Hence, many taxonomists argue in favor of breaking down large genera. For instance, the lizard genus Anolis has been suggested to be broken down into 8 or so different genera which would bring its ~400 species to smaller, more manageable subsets. [20]

See also

Related Research Articles

<span class="mw-page-title-main">Linnaean taxonomy</span> Rank based classification system for organisms

Linnaean taxonomy can mean either of two related concepts:

  1. The particular form of biological classification (taxonomy) set up by Carl Linnaeus, as set forth in his Systema Naturae (1735) and subsequent works. In the taxonomy of Linnaeus there are three kingdoms, divided into classes, and they, in turn, into lower ranks in a hierarchical order.
  2. A term for rank-based classification of organisms, in general. That is, taxonomy in the traditional sense of the word: rank-based scientific classification. This term is especially used as opposed to cladistic systematics, which groups organisms into clades. It is attributed to Linnaeus, although he neither invented the concept of ranked classification nor gave it its present form. In fact, it does not have an exact present form, as "Linnaean taxonomy" as such does not really exist: it is a collective (abstracting) term for what actually are several separate fields, which use similar approaches.
<span class="mw-page-title-main">Binomial nomenclature</span> System of identifying species of organisms using a two-part name

In taxonomy, binomial nomenclature, also called binominal nomenclature or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Such a name is called a binomial name, a binomen, binominal name or a scientific name; more informally it is also historically called a Latin name.

Family is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between order and genus. A family may be divided into subfamilies, which are intermediate ranks between the ranks of family and genus. The official family names are Latin in origin; however, popular names are often used: for example, walnut trees and hickory trees belong to the family Juglandaceae, but that family is commonly referred to as the "walnut family".

<span class="mw-page-title-main">International Code of Zoological Nomenclature</span> Code of scientific nomenclature for animals

The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the International Commission on Zoological Nomenclature. The rules principally regulate:

<i>Incertae sedis</i> Term to indicate an uncertain taxonomic position

Incertae sedis or problematica is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty at specific taxonomic levels is indicated by incertae familiae, incerti subordinis, incerti ordinis and similar terms.

<span class="mw-page-title-main">Botanical name</span> Scientific name for a plant, alga or fungus

A botanical name is a formal scientific name conforming to the International Code of Nomenclature for algae, fungi, and plants (ICN) and, if it concerns a plant cultigen, the additional cultivar or Group epithets must conform to the International Code of Nomenclature for Cultivated Plants (ICNCP). The code of nomenclature covers "all organisms traditionally treated as algae, fungi, or plants, whether fossil or non-fossil, including blue-green algae (Cyanobacteria), chytrids, oomycetes, slime moulds and photosynthetic protists with their taxonomically related non-photosynthetic groups ."

<span class="mw-page-title-main">International Association for Plant Taxonomy</span> Plant biodiversity organization

The International Association for Plant Taxonomy (IAPT) is an organization established to promote an understanding of plant biodiversity, facilitate international communication of research between botanists, and oversee matters of uniformity and stability in plant names. The IAPT was founded on July 18, 1950, at the Seventh International Botanical Congress in Stockholm, Sweden. The IAPT headquarters is located in Bratislava, Slovakia. Its president, since 2017, is Patrick S. Herendeen of the Chicago Botanic Garden; vice-president is Gonzalo Nieto Feliner of the Real Jardín Botánico, Madrid; and secretary-general is Karol Marhold of the Plant Science and Biodiversity Centre, Slovak Academy of Sciences, Bratislava.

Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms. To an end-user who only deals with names of species, with some awareness that species are assignable to families, it may not be noticeable that there is more than one code, but beyond this basic level these are rather different in the way they work.

In botany, the correct name according to the International Code of Nomenclature for algae, fungi, and plants (ICN) is the one and only botanical name that is to be used for a particular taxon, when that taxon has a particular circumscription, position and rank. Determining whether a name is correct is a complex procedure. The name must be validly published, a process which is defined in no less than 16 Articles of the ICN. It must also be "legitimate", which imposes some further requirements. If there are two or more legitimate names for the same taxon, then the correct name is the one which has priority, i.e. it was published earliest, although names may be conserved if they have been very widely used. Validly published names other than the correct name are called synonyms. Since taxonomists may disagree as to the circumscription, position or rank of a taxon, there can be more than one correct name for a particular plant. These may also be called synonyms.

In botanical nomenclature, author citation is the way of citing the person or group of people who validly published a botanical name, i.e. who first published the name while fulfilling the formal requirements as specified by the International Code of Nomenclature for algae, fungi, and plants (ICN). In cases where a species is no longer in its original generic placement, both the authority for the original genus placement and that for the new combination are given.

In zoological nomenclature, the valid name of a taxon is the correct scientific name for that taxon. The valid name must be used for that taxon, regardless of any other name that may currently be used for that taxon, or may previously have been used. A name can only be valid when it is an available name under the International Code of Zoological Nomenclature (ICZN); if a name is unavailable, then it cannot be considered either valid or invalid.

A conserved name or nomen conservandum is a scientific name that has specific nomenclatural protection. That is, the name is retained, even though it violates one or more rules which would otherwise prevent it from being legitimate. Nomen conservandum is a Latin term, meaning "a name to be conserved". The terms are often used interchangeably, such as by the International Code of Nomenclature for Algae, Fungi, and Plants (ICN), while the International Code of Zoological Nomenclature favours the term "conserved name".

In botanical nomenclature, autonyms are automatically created names, as regulated by the International Code of Nomenclature for algae, fungi, and plants that are created for certain subdivisions of genera and species, those that include the type of the genus or species. An autonym might not be mentioned in the publication that creates it as a side-effect. Autonyms "repeat unaltered" the genus name or species epithet of the taxon being subdivided, and no other name for that same subdivision is validly published. For example, Rubus subgenus Eubatus is not validly published, and the subgenus is known as Rubus subgen. Rubus.

In biological nomenclature, a nomen novum, new replacement name is a scientific name that is created specifically to replace another scientific name, but only when this other name cannot be used for technical, nomenclatural reasons. It does not apply when a name is changed for taxonomic reasons. It is frequently abbreviated, e.g.nomen nov., nom. nov..

The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently.

<span class="mw-page-title-main">Taxonomic rank</span> Level in a taxonomic hierarchy

In biology, taxonomic rank is the relative level of a group of organisms in an ancestral or hereditary hierarchy. A common system of biological classification (taxonomy) consists of species, genus, family, order, class, phylum, kingdom, domain. While older approaches to taxonomic classification were phenomenological, forming groups on the basis of similarities in appearance, organic structure and behaviour, methods based on genetic analysis have opened the road to cladistics.

This is a list of terms and symbols used in scientific names for organisms, and in describing the names. For proper parts of the names themselves, see List of Latin and Greek words commonly used in systematic names. Note that many of the abbreviations are used with or without a stop.

<span class="mw-page-title-main">Interim Register of Marine and Nonmarine Genera</span> Taxonomic database

The Interim Register of Marine and Nonmarine Genera (IRMNG) is a taxonomic database which attempts to cover published genus names for all domains of life from 1758 in zoology up to the present, arranged in a single, internally consistent taxonomic hierarchy, for the benefit of Biodiversity Informatics initiatives plus general users of biodiversity (taxonomic) information. In addition to containing over 490,000 published genus name instances as at March 2020, the database holds over 1.7 million species names, although this component of the data is not maintained in as current or complete state as the genus-level holdings. IRMNG can be queried online for access to the latest version of the dataset and is also made available as periodic snapshots or data dumps for import/upload into other systems as desired.

Algospongia is a class of small, calcified fossil organisms of uncertain taxonomic position, assigned in a comprehensive 2010 review to "Animalia" incertae sedis, but both prior to and post that to an unnamed phylum of Algae; other workers simply list them as Problematica. They occur in carbonate rocks of the Paleozoic era and their last representatives occur in the Late Permian geological period. Characteristic genera include Aoujgalia, Moravammina and the early-appearing Wetheredella, although the taxonomic validity of the last named genus has been disputed.

References

  1. 1 2 "ICTV Taxonomy". International Committee on Taxonomy of Viruses. 2017. Retrieved May 29, 2018.
  2. ↑ Sigward, J. D.; Sutton, M. D.; Bennett, K. D. (2018). "How big is a genus? Towards a nomothetic systematics". Zoological Journal of the Linnean Society. 183 (2): 237–252. doi: 10.1093/zoolinnean/zlx059 .
  3. ↑ Gill, F. B.; Slikas, B.; Sheldon, F. H. (2005). "Phylogeny of titmice (Paridae): II. Species relationships based on sequences of the mitochondrial cytochrome-b gene". Auk. 122 (1): 121–143. doi:10.1642/0004-8038(2005)122[0121:POTPIS]2.0.CO;2. S2CID   86067032.
  4. ↑ de la Maza-Benignos, Mauricio; Lozano-Vilano, Ma. de Lourdes; García-Ramírez, María Elena (December 2015). "Response paper: Morphometric article by Mejía et al. 2015 alluding genera Herichthys and Nosferatu displays serious inconsistencies". Neotropical Ichthyology. 13 (4): 673–676. doi: 10.1590/1982-0224-20150066 .
  5. ↑ Stuessy, T. F. (2009). Plant Taxonomy: The Systematic Evaluation of Comparative Data (2nd ed.). New York, New York, US: Columbia University Press. p. 42. ISBN   9780231147125.
  6. 1 2 D. L. Hawksworth (2010). Terms Used in Bionomenclature: The Naming of Organisms and Plant Communities : Including Terms Used in Botanical, Cultivated Plant, Phylogenetic, Phytosociological, Prokaryote (bacteriological), Virus, and Zoological Nomenclature. GBIF. pp. 1–215. ISBN   978-87-92020-09-3.
  7. ↑ "WoRMS - World Register of Marine Species - Physeter Linnaeus, 1758". www.marinespecies.org.
  8. ↑ "WoRMS - World Register of Marine Species - Pecten O. F. Müller, 1776". www.marinespecies.org.
  9. ↑ "IRMNG: Interim Register of Marine and Nonmarine Genera". www.irmng.org. Retrieved 2016-11-17.
  10. ↑ Rees, Tony; Vandepitte, Leen; Vanhoorne, Bart; Decock, Wim (2020). "All genera of the world: an overview and estimates based on the March 2020 release of the Interim Register of Marine and Nonmarine Genera (IRMNG)". Megataxa. 1 (2): 123–140. doi: 10.11646/megataxa.1.2.3 .
  11. ↑ "LPSN - List of Prokaryotic names with Standing in Nomenclature". www.bacterio.net.
  12. ↑ "Index Fungorum Home Page". www.indexfungorum.org.
  13. ↑ "Index Nominum Algarum: names of algae". ucjeps.berkeley.edu.
  14. ↑ "Algaebase :: Listing the World's Algae". www.algaebase.org.
  15. ↑ "Index Nominum Genericorum (ING), Botany, Smithsonian Institution". naturalhistory2.si.edu.
  16. ↑ "International Plant Names Index". www.ipni.org.
  17. ↑ "Nomenclator Zoologicus". ubio.org.
  18. ↑ "Catalogue of Life - 2018 Annual Checklist : 2018 Annual Checklist". www.catalogueoflife.org.
  19. ↑ Frodin, David G. (2004). "History and concepts of big plant genera". Taxon . 53 (3): 753–776. doi:10.2307/4135449. JSTOR   4135449.
  20. ↑ Nicholson, K. E.; Crother, B. I.; Guyer, C.; Savage, J.M. (2012). "It is time for a new classification of anoles (Squamata: Dactyloidae)" (PDF). Zootaxa. 3477: 1–108. doi: 10.11646/zootaxa.3477.1.1 . Archived (PDF) from the original on 2022-10-09.
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